Magnetic recording apparatus



Feb. 7, 195(9 c s 2,496,441

MAGNETIC RECORDING APPARATUS Filed March 9, 1946 [Hz En [UP /'74e w/y Owen J WMW Patented 7,

UNITED ST ENT OF F ICE;

GNETIC JRECQRDINGAPPARATUS Marvin Jami-as; Chicago, 111., assignortoiArmour;

Research: -tFInitiation of Illinois: Institute ofz: Technology; Qhieagg; 111., incorporation of ;.Illi-- nois Application 'Marcltfil; 1946; Seriail No; 6539238 or high frequencycomponent in conjunctiionvwithz the-audio current which is being/recorded ion: a; traveling record medium. Theusual practice is to. demagnetize. the traveling ;.record medium vand thereafter pass the same atraveling recentl -medium through a-magnetic fieldwhichisrestablishedjoyr;1'52

the. joint actionhof a fiuctuatingsignal ofuwhichs a record is to be made, andsarhigfh ifrequency cm'em rent.

One, of the principal ifeaturesrand;zobjectsz ofe the present invention: is to;provide:ainoiiel mage 2i I netic recording method-t and:- means pwherei nzthe. wire ,is subjected-to the -raction of a e-circular frequency -,magnetiq field i at vthe -.-time;;"thatr they fluctuating signalis. being :recorded :by establis'he; inga longitudinal magnetiofield: 1

A further ObjGCU'OfwthGtpliesemiiiIlVGIitiOlliiS-iO-z subject a traveling record mediumztorawliighi frequency field which-lies ina planetransversetothe: longitudinal axis of the traveling-grecordrmediumand simultaneously subject it-etothe -aotion-=-of::a

fluctuating magnetic field disposedsubstantially parallel tothe direction-of, motion'aofgthetravel ing record medium which; is establishedbys the' fluctuating signal energy vofwhich the-record is: to be made.

A still further objects-oftherpresentsinvention is; to demagnetize a travelingrecordmcdiumiin a :plane substantially at rightangles-tto'the longiea tudin a1 axis of the traveling record mediums-and thereafter pass the demagnetizedirecord medium through-a field establishedibythe joint aetion ofv a high frequency currentand a fluctuating-signal current, the high -:frequencycurrent tending to establish a field substantially aat -right angles=- to the longitudinal; axis oftherecord medium and the signal current: tending to establish a field substantially .parallel tothe longitudinal axis of the-r record medium.

Still another and further object of the--present-i diiuniby agcircular magnetic fieldylying in a-pl ne substantially at-right angles to the longitudinal axis 015 stli'e recordzmediumzand thereatterlsubiect the 'jarayelingmeeord mediumtothe joint action of:

zfie di'whieh tends'to be awircula-r held: in aplaneat'fri ht anglessto the longitudinal axis. of the recordi-lmediumzand a second :field which tends to 11.811118. direqtiomparallel 130112116 longitudinal axis 1 of the recordmedium;

111871108761 features which I believe to be chare aoteristic 'of'i'myf inventioniare set forth with par- 1 Myinventiona ticularity in the :appended claims. itseli-rhowever, both-gas to its organization-mane ner ofjconstruction-and method of operation to getherrwith further-objects andadvantages there- 1 ot may best be understoodbyreference-to the following description; takeni-nconnection with the -t aceom-pany-in idrawing; in-.which-:

Figure 1 is'a; diagrammatic sketch of 'one em! bodiment ,ofmy invention whereinna traveling =5 wire nis subjectedto thejoint action-of a circular:

igh::frequencymagnetic field and a longitudin al;-=

fluctuatingsignal field; and

.FigurerZ is a :sehematiaditrgram ora modified 1 *form of myi invention whereinboth theerase fieldn and i he- ;hig-hfrequency wbias" fieldware :circu1ar."-

fields at right-an les to-rthe longitudinal axis-bf;

the traveling record medium;

.In the embodiments of theinventionfillustratedc herein, the. eirculanzfields are established:by -causwing the traveling record-:medium-itseH to carry the i'highirequencyycurrent at: @the point where fit: crosses againrin the. recording head; It has ,-been; found that this does {not interfere with'the-sig-nal-j:

being-i recordedlwhich'xm; anyway is :disadvanfrequencycurrent is -preferab1yroia' frequency sufiiciently :high :that. itcannotfbe resolved-route. 1: the. trarelingrecer'damediumrduring the short' ine terval- 'thatrany particular point 'on: the record mediumis-passing'through the gap.

head 10 I is diagrammaticallyillustratedwhieh is made up of two c-s-h'a-ped halv'es 11 and !-=2-con= In Figure 1 of the drawing-a magneticrecorder necte'd together-at thebase by an insulatingstrip I3 whieh is formed of any-suitable dielectric- Ina-=- invention is to demagnetize-a traveling record="me-- '"*teria"1.- The two' *-C=shaped--members- 'l I' and I2 ciently high to retain a record magnetically recorded thereon.

This wire I8 lies in the slots or grooves l1 and travels in a direction which is longitudinal of its own axis. For example, the wire l8 may be caused to travel from left to right from a supply reel 8 to a take-up reel 9 driven by a motor 1, the direction of travel of the wire being as illustrated by the arrow 19. No means is shown for causing the wire I 8 to travel through the head ID for such means forms no part of the present invention. It will, however, b understood that during the recording process the wire [8 does travel through the head I0, as indicated by the arrow.

A signal coil is mounted on the recording head 10, and in this particular instance has been shown as disposed around the gap 2t which lies between the polar portions [4 and IS. The signal coil 1 0 is connected to the output of an audio amplifier 22 which amplifies a signal current to be recorded. This signal current may be, for example, current obtained from a microphone 23, which is diagrammatically represented as being connected to the input of the audio amplifier 22. From the drawing it will be understood that when fluctuating current flows through the coil 20 a fluctuating magnetic field is established in the gap 2| which is parallel to the direction of motion of the wire l8 as it passes across again;

High frequency current is supplied from a suitable source of high frequency 24 which may, for example, be any suitable form of electronc oscillator. When the signal current is produced by audible sound picked up by the microphone 23 the high frequency current is mixed with it in the head [0. The high frequency source 24 is preferably set to operate at somewhere in the range between 20 to 100'kilocycles. One side of the high frequency source 24 is connected to the t-shaped section II of the recorder head l0 through a high impedance 25. The other side is directly connected to the C-shaped section l2 of the magnetic recorder head l0. Since the dielectric insert |3 prevents the current from crossing between the sections II and I2 to close the load circuit of the high frequency source 24, it will be apparent that th current will travel through the wire l8 at the gap 2 I.

While the wire I8 is continually changing its position as it crosses the gap 2|, it will'be noted that there is always a section of wire lying across the gap 2| which closes the load circuit of the high frequency oscillator 24. The impedance element 2-5 is a load resistance and is of relatively high value in order not to have a direct short circuit across the high frequency source and in order to prevent any substantial changes in the current which might otherwise occur due to changes in contact resistance.

Since the high frequency current is flowing through the wire I8 at the gap 2| in a longitudinal direction, it will immediately be apparent that the magnetic field tends to be established by this flow of current which is a circular magnetic field lying in a plane normal to the longitudinal axis of the wire. The magnetic field thus tends to reverse in a circular direction in a plane at right angles to the longitudinal axis of the wire.

It has been found that a high frequency biasing component at right angles to the recorded signal field produces ver satisfactory results, and this is particularly true where the high frequency field is a circular field.

In Figure 2 of the drawing I have illustrated a modified form of the present invention wherein a circular field is also used to demagnetize the wire. In this illustrated embodiment of the modified form of the invention, a recorder head 26 is provided which is made up of an I-shaped center leg 21 and two straight upstanding outer legs 28 and 29. The outer leg 28 is physically connected to the center leg 27 through an insulating block 39. Similarly, the other outer leg 29 is connected to the center leg 21 through an insulating block 3|. These insulating blocks 30 and 3! may be of any suitable dielectric material.

The top of the I-shaped center section 21 includesa polar portion 32 and a polar portion 33 which extend, respectively, toward the outer legs 28 and 29, but stop just short thereof to provide non-magnetic gaps 34 and 35. It will be noted that the gap 34 is slightly larger than the gap 35 and this is desirable since the gap 34 is the gap used to demagnetize the wire, while the gap 35 is the one used to record a signal on the wire. The top of the recorder head 26 is grooved to receive the wire l8 by providing suitable grooves 36, 31 and '38 in the legs 28, 21 and 29 respectively. Means (not shown) is provided to cause the wire iii to travel through the head 26 in the direction indicated by the arrow 39.

The voice coil 20, in this case, is mounted on the upstanding leg 29, and is connected to the output of the audio amplifier 22 which in turn is connected to a microphone 23, as described in connection with Figure 1.

The high frequency source 24 is connected to a voltage divider or potentiometer 40 which is preferably grounded as at 4| at its lower end. The grounded lower end of the potentiometer is connected through a conductor 42 of the center leg 2'l'of the head 26. The leg 28 of the head 26 is connected from a movable contact element 43 on the potentiometer 40 through a load impedance 44. The leg 29 is connected from a movable contact 45 on the potentiometer 40 through a load impedance 46. Since the current which is necessary to erase or demagnetize the wire I8 must be substantially greater than the current which is desired to supply the high frequency for the recording process, the voltage applied across the legs 28 and 21 must be substantially greater than the voltage'applied across the legs 29 and 21. This is done by the movable contact elements 43 and 45 on the potentiometer 40.

From'the above description it will be apparent that'as the wire l8 travels across the gap 34 it is demagnetized by a high frequency circular magnetic field established by the flow of high frequency current through the portion of the wire which is lying betwen the polar portion 32 of the center leg 21 and the upstanding leg 28. It is thereafter magnetically recorded on by passing it through a magnetic field in the gap 35 which is established by the joint action of the longitudinalmagnetic field set up by the signal coil 20 and the circular high frequency magnetic field set up by the high frequency current flowing through the wire itself in the gap 35.

While in the preferred formlof the invention the high frequency current flows through the Wire, the process may be reversed and the audio current may flow through the wire.

While I have shown a particular embodiment of my invention, and described a particular method of operation, it will, of course, be understood that I do not wish to be limited thereto, since many modifications may be made and I therefore contemplate, by the appended claims, to cover all such modifications as fall within the true spirit and scope of my invention.

- I claim as my invention:

1. Means for magnetically recording fluctuating signal energy on a traveling elongated magnetizable record member comprising a magnetic recording head including a core having a pair of confronting polar portions spaced to form a non-magnetic gap therebetween through which said member travels from one polar portion to the other, a signal coil, means for energizing said coil with fluctuating electric energy representing the signal to be recorded, said signal coil being mounted on said core in such a position as to produce a fluctuating magnetic field in said gap when said coil is energized, said core being separated at a second point remote from said gap so as to form two parts electrically separated from each other and each including one polar portion, and means for connecting said parts to opposite sides of a source of high frequency current, whereby high frequency current flows through the portion of said record member which is spanning said gap.

2. Means for magnetically recording fluctuating signal energy on a traveling elongated magnetizable record member comprising a magnetic recording head including a core having a pair of confronting polar portions spaced to form a nonmagnetic gap therebetween through which said member travels from one polar portion to the other, a signal coil, means for energizing said coil with fluctuating electric energy representing the signal to be recorded, said signal coil being mounted on said core in such a position as to produce a fluctuating magnetic field in said gap when said coil is energized, said core being separated at a second point remote from said gap so as to form two parts electrically separated from each other and each including one polar portion, an insulating block of dielectric material between said parts and said separated point, a source of high frequency current, a load resistance, said source of high frequency current being connected to said parts through said load resistance, whereby high frequency current flows through the por tion of said record member which is spanning said gap as it travels thereacross.

3. Means for magnetically recording fluctuating signal energy on a traveling elongated magnetizable record member comprising a magnetic recording head including a core of magnetic material of low retentivity, said core being formed of two C-shaped portions positioned in confronting relationship with their legs in spaced confronting relationship to define a magnetizing gap and a second gap, said second gap being filled by an electrical insulating block, said recording head being arranged to have said traveling record member pass therethrough across said first gap, a signal coil wound around at least one of said C-shaped core member parts, means for energizing said coil with fluctuating electric energy representing the signal to be recorded, a load re- 6 sistance, a source of high frequency current, means for connecting one side of said source of high frequency to one of said C-shaped parts, and the other side of said source of high frequency through said'load resistance to the other of said C-shaped parts.

4. Means for magnetically recording fluctuating signal energy on a traveling elongated magnetizable record member comprising a magnetic recording head including a core of low retentivity magnetic material formed in three parts electrically separated from each other and including two pairs of polar portions spaced to provide an erasing gap and a recording-gap, two of said polar portions being on one of said core parts, said traveling elongated record medium being arranged to pass first across said erase gap and then across said recording gap, means for connecting a source of high frequency electric current directly to said polar portions defining said erase gap, means for connecting a high frequency current of lower amplitude than said first high frequency current directly to said polar portions defining said recording gap, a signal coil mounted on said recording head, means for energizing said coil with fluctuating electric energy representing the signal to be recorded, said signal coil being mounted on said core in such a position as to produce a fluctuating magnetic field across said recording gap when said coil is energized.

5. A magnetic recorder comprising a recorder head through which an elongated magnetizable record member is arranged to pass, said head including an I-shaped center leg and an outer leg on either side of said I-shaped center leg, said outer legs being electrically separated from said center leg at the bottom and being spaced from said center leg at the top to form a demagnetizing gap and a recording gap, 8, signal coil wound around said outer leg which is spaced from said center leg to define said recording gap, means for energizing said signal coil with fluctuating electric energy, and whose highest frequency is low enough to be resolved by said recording gap, a source of high frequency, a potentiometer connected across said source of high frequency and having one end thereof grounded, a pair of load resistances, a pair of movable contacts on said potentiometer, one of the outer legs of said recorder head being connected through one load resistance to one movable contact and the other outer leg being connected through the other load resistance to the other movable contact, whereby high frequency current of relatively high magnitude may be caused to pass through the portion of said record member spanning said erase gap and relatively low magnitude high frequency current is caused to pass through the portion of said record member spanning said recording gap.

6. Means for magnetically recording a signal on a traveling magnetizable record medium comprising a magnetizable record medium, means for setting up a fluctuating signal magnetic field, means for superimposing on said first field and oriented at a right angle thereto a fluctuating magnetic field of higher frequency, and means for passing said record medium through said superimposed magnetic fields, one of said magnetic fields being substantially parallel to the direction of travel of the wire.

'7. Means for magnetically recording a signal on a traveling magnetizable record medium comprising a magnetizable record medium, means for setting up a; fluctuating. signalw magnetic: field; means. for superimposing; a fluctuating circular magnetic; field of higher frequency: on said first: field, and at a right angle thereto, said secondfield: lying in a plane substantially normal to the; direction of travel of the liEOOIdA medium, and

means, for passing saidrecord' medium; through said. superimposed magnetic fields CAMRASZ REFERENCES- CITED The following references are of record inthe.

file. of this patent:

UNITED swa ms rams Nilmber Number Name Date Nakken- Mar. 5, 1935 Camnas. v.Iune 131 1944 Camras Iune 13', 1944. Camras .June 13, 1944' S'unstin Aug. 5, 1947' Sunst'ein Jan. 4', 1949 FOREIGN PATENTS" Gountry Date France Oct. 24,, 1930 *Germany Max-12431934 

